console.log
in there or set a breakpoint and expect to find the bug. Agent execution is non-deterministic; you can run the exact same prompt twice and get two different tool-call sequences. By the time an agent crashes or gives a hallucinated answer, the actual "decision" that caused the failure happened five turns ago in a hidden reasoning chain.If you want to actually fix your AI workflow, you have to stop looking at the output and start obsessing over the execution transcripts.
Why your agent is actually breaking #
After spending a lot of time with Claude Code, I've noticed that almost every "random" failure falls into one of these three buckets:
Silent Context Overflow: The agent hits the token limit, but instead of crashing, it just "forgets" the critical instruction from the start of the session.Schema Hallucinations: The model invents a field name that doesn't exist in your tool's JSON schema, leading to a tool error that the agent then tries (and fails) to "fix" by guessing again.Reasoning Loops: The agent gets stuck in a cycle where it calls Tool A, gets an error, decides to try Tool A again with a slight variation, and repeats this until the budget runs out.
How to trace tool calls effectively #
To get a real handle on this, you need a deep dive into the transcripts. A proper trace isn't just a log of what happened; it's a record of the assistant's reasoning before the tool call.
When I'm debugging, I look for the gap between the "Thought" and the "Action." If the thought says "I need to check the user's email" but the tool call is getUserData({ id: 'null' })
, you don't have a tool bug—you have a prompt engineering problem where the model isn't extracting the ID correctly.
Tooling for observability #
Depending on where you are in the dev cycle, different tools hit differently:
LangSmith: Best for deep trace inspection when you're trying to figure out exactly why a specific production request went sideways.Arize Phoenix: Great for local iteration because it doesn't require as much cloud overhead.Braintrust: This is the way to go if you're doing eval-driven debugging (comparing version A of a prompt vs version B).
For those who want full control, building a custom trace analyzer in TypeScript is the move. You can write scripts to scan thousands of logs for specific patterns, like "how many times did the agent call the same tool three times in a row?"
Pro tip for meta-analysis #
If you have a mountain of logs, don't read them manually. Feed the structured traces back into a separate LLM instance. Use a prompt that forces the model to separate the symptom (e.g., "The agent failed to update the database") from the root cause (e.g., "The agent misinterpreted the date format in the tool output"). This turns a week of manual log digging into a ten-minute summary. Next Who actually needs a heavy framework for a landing page? →